c-Jun can recruit JNK to phosphorylate dimerization partners via specific docking interactions

Area of Science:

• Molecular Biology
• Biochemistry
• Cell Signaling

Background:

• Structurally similar serine/threonine kinases exhibit distinct substrate specificities in vivo despite recognizing similar peptide motifs in vitro.
• The Jun kinases (JNKs) are a family of stress-activated protein kinases involved in various cellular processes.
• Jun proteins (c-Jun, JunB, JunD) are transcription factors that are targets of JNK signaling.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying the substrate specificity of JNKs towards different Jun proteins.
• To identify the roles of docking sites and specificity-conferring residues in JNK-mediated phosphorylation.
• To investigate the impact of protein-protein interactions, such as heterodimerization, on kinase-substrate recognition.

Main Methods:

• In vitro kinase assays to measure phosphorylation efficiency.
• Analysis of Jun protein sequences to identify docking sites and phosphoacceptor residues.
• Site-directed mutagenesis to introduce or remove specificity-conferring residues.
• Studies on Jun protein heterodimerization.

Main Results:

• JNKs efficiently phosphorylate c-Jun, less efficiently phosphorylate JunD, and do not phosphorylate JunB.
• A functional JNK docking site and specificity-conferring residues are crucial for efficient JNK substrate recognition.
• JunB possesses a docking site but lacks specificity residues, explaining its lack of phosphorylation.
• JunD, lacking a docking site but having a c-Jun-like phosphoacceptor, can be phosphorylated via heterodimerization with docking-competent partners.

Conclusions:

• Kinase substrate specificity is determined by both phosphoacceptor site recognition and additional docking interactions.
• Heterodimerization is a mechanism by which JNKs can recognize and phosphorylate substrates lacking direct docking sites.
• These findings provide insights into the regulation of signal-regulated protein kinase activity and transcription factor function.